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29 CHEMICAL SIGNALING WITHIN THE ANIMAL BODY
EXTENDED LECTURE OUTLINE
The Neuroendocrine System (p. 638)
29.1
29.2
Hormones (p. 638; Figs. 29.1, 29.2)
A. The diverse activities of the human body must be coordinated, and the central nervous system
uses both nervous impulses and chemical messages to accomplish that task.
B. The chemical signals used in the body are called hormones and are produced in a given gland
or organ and travel through the bloodstream to a distant target.
C. There are a number of advantages to controlling the body using hormones rather than nervous
impulses.
D. Endocrine glands are the hormone-producing glands of the body and secrete their chemical
signals directly into the bloodstream.
E. By contrast, exocrine glands secrete their products into ducts, such as sweat glands.
F. Because the endocrine system and the motor nervous system are the means the central
nervous system uses to control the body, they are often considered one system, called the
neuroendocrine system.
G. The Chain of Command
1. We now know that the hypothalamus initiates the production of hormones by the pituitary
gland.
H. How Hormones Work
1. Hormones operate by traveling through the bloodstream to particular cells that receive
them using receptor proteins in their cells.
2. The path of communication taken by a hormonal signal involves issuing the command,
transporting the signal in the bloodstream, hitting the target, and having an effect.
How Hormones Target Cells (p. 270; Figs. 29.3, 29.4, 29.5)
A. Steroid Hormones Enter Cells
1. Steroid hormones are lipid soluble and pass easily through the target cell's membrane
into the cytoplasm where they meet up with a protein receptor.
2. A hormone-receptor complex forms, entering the nucleus of the cell and attaching to
specific regulatory sites along the DNA of the cell.
3. Specific genes are produced, and the actions of the cell are altered.
4. The body synthesizes its steroid hormones from molecules of cholesterol.
5. Estrogen, progesterone, and testosterone, hormones linked to sexual traits, are all
steroids.
6. Anabolic steroids are used by athletes to increase muscle mass and enhance athletic
performance.
7. Many adverse side effects, such as heart disorders and liver cancer, are associated with
the use of these illegal steroids.
B. Peptide Hormones Act at the Cell Surface
1. Peptide hormones cannot pass through cell membranes.
2. The receptors for these types of hormones are located within the cell membranes of
target cells.
3. The hormone-receptor complex then triggers a chain of events in the cytoplasm in which
a second signal molecule, the second messenger, is involved.
4. Second messengers work by activating enzymes in the cell, such as protein kinases,
which in turn can produce many product molecules.
5. The second messenger, such as cyclic AMP or Ca++, amplifies the response of a cell after
it has received a peptide hormone.
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The Major Endocrine Glands (p. 642)
29.3
29.4
29.5
The Hypothalamus and the Pituitary (p. 642; Figs. 29.6, 29.7, 29.8, 29.9)
A. The pituitary gland, located in a bony recess below the hypothalamus, is actually two separate
glands, the posterior pituitary and the anterior pituitary.
B. The Posterior Pituitary
1. The posterior pituitary is under nervous control by the hypothalamus, and releases two
hormones.
2. The first is antidiuretic hormone (ADH), also known as vasopressin, and targets the
kidney and helps conserve water.
3. The second hormone, oxytocin, is released to initiate uterine contractions during
childbirth and when the infant suckles at the breast, triggering a letdown of milk.
C. The Anterior Pituitary
1. The anterior pituitary is controlled by hormones released from the hypothalamus, and
produces seven separate peptide hormones.
2. Growth hormone (GH), or somatotropin, is produced in tiny amounts and stimulates
growth during childhood and puberty.
3. Thyroid-stimulating hormone (TSH) stimulates the thyroid gland to release its
metabolism-stimulating hormones.
4. Luteinizing hormone (LH) triggers ovulation in females and helps to develop and
maintain secondary sexual characteristics in males.
5. Follicle-stimulating hormone (FSH) stimulates the testes to produce sperm and helps the
ovaries produce mature egg cells.
6. Adrenocorticotropic hormone (ACTH) stimulates the adrenal gland to release hormones
that regulate the conversion of fat into glucose, sodium and potassium balance, and male
secondary sexual characteristics.
7. Prolactin stimulates milk production in mammary glands.
8. Melanocyte-stimulating hormone (MSH) initiates color changes in the skin of
amphibians and reptiles; its role in the human is poorly understood.
D. How the Hypothalamus Controls the Anterior Pituitary
1. Releasing hormones from the hypothalamus travel to the anterior pituitary via the
hypothalamo-hypophyseal portal system.
2. Mostly the secretions from the anterior pituitary are controlled through negative feedback
inhibition.
The Pancreas (p. 645; Fig. 29.10)
A. The pancreas secretes digestive enzymes as well as two hormones, insulin and glucagon.
B. Insulin signals cells to take up more glucose to lower blood glucose levels, while glucagon
mobilizes glucose reserves to raise blood glucose; together, these two hormones carefully
regulate the levels of glucose in the blood.
C. Diabetes is a condition in which levels of glucose in the blood become too high.
D. Type I diabetes is an autoimmune disease in which antibodies attack beta cells of the
pancreas, resulting in lowered levels of insulin.
E. Type I diabetes occurs most often in people under the age of 20, and must be treated with
daily injections of insulin.
F. Type II diabetes occurs mostly in overweight people over the age of 40.
G. Because of too much sugar and calories in the diet, the body dismantles some of its insulin
receptors.
H. The pancreas attempts to put out more insulin to lower the levels of glucose in the blood.
I. Type II diabetes can be treated with proper diet and medications.
The Thyroid, Parathyroid, and Adrenal Glands (p. 646; Figs. 29.11, 29.12; Table 29.1)
A. The Thyroid: A Metabolic Thermostat
1. The thyroid gland can be considered the body's thermostat of metabolism.
2. It produces iodine-containing thyroxine that is essential for normal metabolic rates and
for development in children.
3. Without it, mental retardation and cretinism result.
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4.
29.6
Calcitonin helps regulate the levels of calcium in the blood; when too high, it lowers the
calcium in the blood by helping bones absorb more calcium.
B. The Parathyroids: Builders of Bone
1. The parathyroid glands are four small glands lying on the back of the thyroid.
2. Their release of parathyroid hormone (PTH) is critical to survival.
3. PTH raises blood levels of calcium when they become too low by mobilizing calcium
reserves from bone and by increasing calcium reabsorption in the kidneys.
4. Calcium is essential for muscle contraction, and the heart cannot survive without it.
C. The Adrenals: Two Glands in One
1. The adrenal glands lie atop each kidney, and consist of a medulla and an outer cortex.
D. The Adrenal Medulla: Emergency Warning System
1. The adrenal medulla releases adrenaline (epinephrine) and norepinephrine that prepare
the body for defense and flight.
2. These two hormones increase the heart rate, blood pressure, blood sugar, and amount of
blood flowing to the lungs and heart.
E. The Adrenal Cortex: Maintaining the Proper Amount of Salt
1. The adrenal cortex produces cortisol and aldosterone.
2. Cortisol stimulates glucose metabolism and helps to reduce inflammation.
3. Aldosterone acts on the kidney to promote retention of salts from the urine.
4. Aldosterone is essential to survival, since nerve impulse conduction and muscle
contraction both require an ample supply of sodium ions.
A Host of Other Hormones (p. 650; Fig. 29.13)
A. Sexual Development
1. The ovaries and testes produce hormones responsible for regulating sexual development
and the reproductive cycle.
B. Other Hormones
1. A number of nonendocrine tissues produce hormones, including the thymus, heart,
kidneys, and skin.
C. Molting and Metamorphosis in Insects
1. Molting hormone, or ecdysone, and juvenile hormone regulate the timing of molting and
metamorphosis in insects.
LEARNING OBJECTIVES
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Understand what hormones are and their advantages over nervous impulses when controlling some
aspects of body functions.
Contrast the functions of endocrine and exocrine glands.
Explain how the hypothalamus controls the secretions of many other endocrine glands.
Describe the mode of action of steroid hormones.
Explain how receptor cells amplify the action of peptide hormones.
Understand that the pituitary gland actually represents two glands.
Know the posterior pituitary hormones and their effects.
List the anterior pituitary hormones and their functions.
Explain how pancreatic hormones regulate blood glucose levels.
Describe the functions of the thyroid hormones.
Explain why we cannot live without parathyroid hormone.
List the hormones of the adrenal medulla and cortex, and tell their functions.
Describe the location of the pineal gland and list the hormone it produces.
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KEY TERMS
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hormone (p. 638) a chemical messenger produced by one part of the body and targeted at another part
endocrine gland (p. 638) Completely enclosed by tissue with no ducts to the outside, these glands are
the hormone producers.
neuroendocrine system (p. 638) The nervous and endocrine systems are so closely linked that they are
sometimes referred to as the neuroendocrine system.
steroid hormone (p. 640) a lipid-soluble molecule synthesized from cholesterol
anabolic steroid (p. 640) a synthetic compound resembling testosterone
peptide hormone (p. 640) hormones with short peptide chains
second messenger (p. 640) a chemical messenger generated after the cell receives a peptide hormone
pituitary gland (p. 641)
negative feedback inhibition (p. 644) Most hormonal secretions are controlled in this manner.
diabetes mellitus (p. 645) a serious metabolic disorder involving high levels of glucose in the blood
thyroid gland (p. 646)
parathyroids (p. 646)
adrenal glands (p. 647)
molting hormone (p. 650) in insects
LECTURE SUGGESTIONS AND ENRICHMENT TIPS
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3.
How Chemicals May Be Related to Breast Cancer. Have your students read the Scientific American
article by D. L. Davis and H. L. Bradlow entitled “Can Environmental Estrogen Cause Breast Cancer?”
October 1995, pages 166–72. Pesticides applied to control insect populations filter into our food and
water supplies. These “xenoestrogens” mimic estrogen in the body and are believed to be contributing
to the phenomenal rates of breast cancer in North American women, as well as to the demise of
amphibian populations and the incidence of sterility in human males. Discuss this article with your
students and have them come up with recommendations to ameliorate the problem.
Why Are We Afraid? Read and discuss N. Kalin's article entitled “The Neurobiology of Fear,”
Scientific American, May 1993, pages 94–99. This article describes where fear is located in the brain,
and discusses the hormonal responses to this emotion.
Steroid Abuse. Using steroids to build muscle tissue and increase athletic performance has become very
popular, and is also very dangerous. Anabolic (tissue-building) steroids can be taken safely in low
dosages prescribed for certain illnesses, such as chronic allergies and rheumatoid arthritis. But certain
athletes have taken these in dosages considerably higher than normally recommended to build muscle
tissue and endurance. Although illegal in this country, anabolic steroids are smuggled in, and as many
as several million athletes have used them. Anabolic steroids are especially dangerous for teenagers
who inject them to “bulk up” with muscles. Death from steroids can occur as early as 20 to 30 years
after using them for as short a period as two or three months. Some of the side effects of anabolic
steroids are:
• increased aggressiveness
• kidney disease and fluid retention
• severe acne
• hair on the face and chest in women
• atrophy of breasts and deepening of the voice in women
• balding in both men and women
• reduced size of testes, impotence, and reduced sperm count
• high cholesterol and high blood pressure leading to heart damage
• liver disease and cancer
• stunted growth of the long bones
• amenorrhea
• delusions and hallucinations
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CHANGES TO THE NEW EDITION
Refer to the Johnson instructor web site at http://www.mhhe.com/biosci/genbio/tlw4 for a complete list of
changes to this edition.
CRITICAL THINKING QUESTIONS
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If dietary calcium is adequate, why is it said that we cannot live without parathyroid hormone?
Make a list of the hormones of the human body that are similar in function to the plant hormones you
studied earlier in this text.
Since the complex multicellular eukaryotes, such as vertebrates and plants, have hormones that control
growth and certain aspects of reproduction, speculate about what group of organisms is most likely to
have been the first to evolve similar hormones.
FILMS/MEDIA SUGGESTIONS
(Telephone and fax numbers and/or web sites for the sources of the following materials are listed in the
Appendix.)
Homeostasis. This video shows an athlete during a marathon race and how his body must react to maintain
homeostasis. How blood sugar and water balance are regulated along with the role of hormones and
feedback mechanisms are examined. 1995. 20 minutes.
Films for the Humanities and Sciences, #AFW5990; also Carolina Biological Supply, CE-49-3706
Glands and Hormones. From The Body Atlas series, this video examines chemical communication within
the body and explores the “fight-or-flight” response. 25 minutes.
CLEARVUE/eav, WW6VH 2201
The Endocrine System. The regulatory functions of the endocrine system and how it interacts with the
nervous system are the main focus of this video. Part of the Human Body Systems Series. 17 minutes.
CLEARVUE/eav, WW6VH 4324
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